1. Field of the Invention
The present invention pertains to the art of cooking and, more particularly, to an oil-based fryer system designed for use in a high heat input rate, a high temperature range, with a minimal amount of oil, to perform rapid cooking operations.
2. Discussion of the Prior Art
Oil-based frying is commonly used as a cooking method for a wide range of food. Of particular interest to the present invention is the use of fryers in fast food restaurants to cook various food items. Compared to preparing drinks and assembling burgers and sandwiches, frying is a time consuming process. The cooking of french fries is of particular concern due to their associated short holding times. More specifically, it is generally desired to limit the time, between cooking of the fries and the selling thereof, to be in the order of seven to ten minutes. If longer holding times are permitted, customer dissatisfaction can ensue due to poor product quality which, in turn, can negatively affect the business and its reputation. Due to these time constraints, it is often necessary to cook new fries to order, which typically takes from 2½ to 4 minutes, plus time for salting, bagging and serving. As a result, the serving of french fries represents the most common source of customer waiting time delays in fast food restaurants.
To address these concerns, a typical fast food restaurant may have up to three fryers in place to minimize delays, particularly during peak business hours. During off-peak hours, the same number of fryers would obviously not be needed. Of course, whenever the fryers are on, a degrading of the oil occurs, sometimes without a corresponding production of a commercially viable product. In general, the quality of the oil in a deep fat fryer will inherently degrade continuously over time, eventually reaching a level that affects the quality of the product in an unacceptable manner. The general practice in the food service industry is therefore to dispose of vats of oil used for deep fat frying on a regular basis, ranging from daily to weekly. Oil cost is in fact one of the largest components of the total operating expense for fried products. Of course, a certain amount of that cost is unavoidable as the oil becomes part of the product being sold, generally in the order of 15% of the final product weight.
When cooking french fries, there are two major processes taking place. In the center of the french fry, the potato is cooked in a manner similar to boiling, with raw potato flavors being stripped out by steam. Steam is generated in the core itself and leaves the french fry through pores in the potato. Physical chemistry dictates that the temperature of the core cannot rise above about 212° F. On the other hand, moisture at the outer surface of the french fry will have evaporated to dry out the potato, so the temperature can approach that of the oil itself. At these temperatures, typically at approximately 300°–350° F., the potato is essentially being toasted and the characteristics that distinguish french fries from boiled potatoes are produced. Toasting is primarily a chemical process which rapidly accelerates as temperature increases.
Although increasing the temperature of the oil is known to reduce the necessary frying time, known fryers have a practical upper limit. That is, at some point, toasting would occur so fast that the outer surface of the potato would bum before the raw potato flavors can be stripped from the core. In addition, use of any higher temperatures would inherently speed up the degradation of the cooking oil which limits the useful lifetime of the oil in the fryer. Because of oil degradation, and the economics of disposal, frying is rarely done above 375° F. For french fries, cooking oil is typically kept at 350° F. or less.
In addition, during the course of cooking a batch of french fries, the temperature of the cooking oil will dip down as much as 50° F. Because of this drop, a graph of oil temperature versus time over such a cooking operation is often referred to as a “U-curve” (see enclosed FIG. 6). The precipitous drop in temperature is a result of melting and/or vaporizing the large quantity of free moisture present in the original french fries. Actually, more than three-quarters of the total energy required to cook fries is consumed by vaporizing/melting, with approximately half of this energy being expended in essentially the first 10–15 seconds of the cooking operation. This oil temperature drop does not stop until vaporization is balanced or exceeded by heat arrival to the fries, which depends on a combination of heat input to the fryer and dispersion of the heat throughout the oil. When the temperature drop of this U-curve is considered, it can be seen that the amount of cooking time improvement that can be achieved through raising oil temperature in current fryers is small.
Attempts have been made in the prior art to reduce cook times in fryers, as well as to extend the useful life of the oil. To this end, it has been proposed in the art to provide a recirculation system for a fryer wherein the oil can be continuously or periodically filtered. At the same time, slightly elevated operating temperatures of the oil can be achieved. However, regardless of these attempted improvements, the technology utilized in connection with commercial fryer arrangements, particularly those found in fast food restaurants, have not changed for quite a lengthy period of time. More specifically, cook times generally in the order of, say three minutes for typical ¼″ shoestring french fries are still employed almost invariably throughout the industry. Therefore, there still exists a need in the art for an improved oil-based fryer system which can significantly reduce the associated cook time, while reducing or eliminating oil disposal, thereby representing significant efficiency and cost effective advantages in the industry. In addition, such a rapid cooking fryer arrangement should minimize the actual number of fryers needed to produce a given output, thereby reducing not only initial expenditures for machinery, but also representing cost savings associated with reduced spacing needed for the machines.